Wikipedia:Reference desk/Archives/Science/2010 June 26

= June 26 =

Cobalt (III) oxide
What is the oxidation state of cobalt in Co3O4? --478jjjz (talk) 03:04, 26 June 2010 (UTC)
 * Both +2 and +3 as the article title suggests ie Co3O4 links to Cobalt(II,III) oxide, the II and III are roman numerals - it's Stock nomenclature. 77.86.115.159 (talk) 03:26, 26 June 2010 (UTC)


 * If cobalt's oxidation number is +2, then Co3+2 O4-2; so the net charge is 6-8 = -2.  However, this can't be because the net charge is supposed to be 0.--478jjjz (talk) 03:37, 26 June 2010 (UTC)

--- For cobalt (III) oxide

If cobalt's oxidation number is +3, then Co3+3 O4-2; so the net charge is 9-8 = +1.--478jjjz (talk) 03:46, 26 June 2010 (UTC)
 * Seriously, read the article - Cobalt's charge is 2 and 3 - that is one third have charge 2, and two thirds have charge 3 - ie it's Co2+(Co3+)2 (O2-)4 . It has the spinel structure, the spinel article has more information.77.86.115.159 (talk) 03:52, 26 June 2010 (UTC)
 * I didn't know that one element could have 2 different oxidation states in one compound. Thank you. "Co2+(Co3+)2 (O2-)4" was extremely helpful.--478jjjz (talk) 04:06, 26 June 2010 (UTC)

N2H4O3 or NH4NO3 might be an example for nitrogen.--Stone (talk) 07:58, 26 June 2010 (UTC)
 * Other well known examples are magnetite, Fe2+(Fe3+)2 (O2-)4, and Prussian blue, (Fe3+)4([FeII(CN)6]4−)3. Prussian blue, or iron(III) hexacyanoferrate(II) is particularly interesting because there is another compound, traditionally called Turnbull's blue, which is iron(II) hexacyanoferrate(III), (Fe2+)4([FeIII(CN)6]4−)3. It turns out that the two compounds are the same: you cannot tell which iron atoms are iron(II) and which are iron(III) in the compound. Physchim62 (talk) 10:50, 26 June 2010 (UTC)
 * That Turnbull formula looks weird: hexacyanoferrate(III) would be a 3− not 4− anion? Iron(II) hexacyanoferrate(III) would be (Fe2+)3([FeIII(CN)6]3−)2 The prussian blue section is an interesting example of how important it is to document the experimental method:) But it also does state not that so-called Turnbull's blue (the preparative method) is iron(III) hexacyanoferrate(II), but instead that it rapidly converts by electron exchange to become it (from the other oxidation-state form). And that there is good evidence which iron oxidation state is in the cyanide complex and which is the counter-cation. DMacks (talk) 16:57, 26 June 2010 (UTC)

Alpha Centauri at 1 G acceleration
How long would it take to reach Alpha Centauri on a ship that accelerated at one G (about 9.8 meters per second per second) for half the trip then spent the last half decelerating at that same rate. Would it even be possible to maintain that rate of acceleration for that long without crossing the speed of light?

I ask this because this would be a convenient way to make "artificial gravity" during the transit. Seems like it would make life a lot easier for the passengers.

63.245.168.34 (talk) 03:25, 26 June 2010 (UTC)
 * The speeds and distances associated with continuous 1G acceleration in space have been frequent topics on the Science Reference Desk. At, for instance, I linked to a site with a relativistic calculator. It sems to be defunct. but the Internet Archive Wayback Machine lets us regress in time (so to speak) to a version from May 2008 which lets you input variables and derive the info you seek.Alpha Centauri is 4.365 light years away (per the Wikipedia article. The webpage says 4.3 light years). The calculator says the trip would take just under 6 years to an observer left behind on Earth, but only 3.58 years as experienced by a traveller on the ship, which would reach a max speed of .952C. Sure the artificial gravity would make life easy for those on board, but figuring out how to build an engine to provide 1G acceleration for 3.58 years would make life a living hell for the engineers assigned the task of designing it and the persons required to pay for building it. Edison (talk) 04:02, 26 June 2010 (UTC)


 * As far as "crossing the speed of light", it would take an infinite amount of energy for any particle to reach the speed of light. See Speed of light.  Comet Tuttle (talk) 05:30, 26 June 2010 (UTC)
 * Okay, this leads to a point I've been confused about for a while. When you think of a normal "constant acceleration", you think of an acceleration due to a constant force. At low speeds, a constant force will yield a constant acceleration as expected. However, when you approach relativistic speeds (as you do in this case), it requires a larger and larger force, and eventually becomes impossible, to maintain a constant acceleration. So the question of "constant 1g acceleration" is not really all that simple. I don't understand how the calculator that Edison linked to accounts for this; can anyone shed some light on this?- Running On Brains (talk) 06:40, 26 June 2010 (UTC)
 * I presume it doesn't. It isn't a 'practical relativistic calculator' just a 'relativistic calculator'. It presumes you are capable of building a ship capable of reaching '.952C' (or whatever maximum speed for your distance), in other words capable of accelerating at a constant 1G for your travel distance, and surviving that travel. Whether it's likely to be possible is besides the point of the calculator Nil Einne (talk) 07:11, 26 June 2010 (UTC)
 * Edit: In fact as I somewhat expected it says "Note how the kinetic energy becomes extremely large. Besides this, there are many other practical problems in realizing a star ship (such as hitting small dust particles while moving at relativistic velocities)" and the site does in fact show the maximum kinetic energy as one of the results which in this case is 202430223928 megajoules per kilogram. Nil Einne (talk) 07:14, 26 June 2010 (UTC)


 * Actually, it doesn't require a larger and larger force (if you deplete fuel, it actually takes less force). What you're thinking of is what's required to maintain a constant 1g acceleration in the original frame of reference.  But that isn't possible; that would eventually put you over the speed of light.
 * In this context, when we talk about a "constant 1g acceleration", we mean in the ship's frame of reference. Assuming the ship's (rest) mass remains constant, that requires only constant force (again, force as measured in the ship's frame).
 * So if you had some magical source of constant force, you could indeed do this, ignoring as Nil says the hazards of your environment.
 * But no one knows of any such source. If you carry fuel with you, you'll run out.  The Bussard ramjet is an idea for getting fuel from surrounding space, but apparently the current consensus is that it probably won't work (though I tend to be skeptical of that sort of prediction when the limitations all appear to be "engineering difficulties" rather than genuine physical limits).  Even with the Bussard ramjet, though, you eventually hit some sort of limit, because the fuel keeps coming at you faster and faster, and eventually the force you have to apply to it to keep it in the reaction chamber is going to equal the outgoing thrust. --Trovatore (talk) 07:28, 26 June 2010 (UTC)
 * How much matter would have to be converted to energy to produce the calculated 202430223928 megajoules per kilogram of kinetic energy? It should be E/C2 but units can be a stumbling block. Dividing 2.02 E17 joules by (3E8 m/sec2)2, I get 2.24 kilograms. Then double that, because you have to decelerate, so 4.48 kg of mass would have to be converted to energy to accelerate a 1 kg payload over the specified voyage. How long would it take the Sun to produce enough energy to accelerate that one kg if all the Sun's output were used to drive the spacecraft? Sun says it converts 4.26 E6 metric tons of mass to energy per second. A tiny fraction of the Sun's output from departure to midpoint would produce the specified acceleration over that timespan. It looks like .024 kg per second of matter converted to energy would power the voyage of a million kilogram spacecraft. (Maybe the folks at Alpha Centauri would power the deceleration after the midpoint turnaround). (Note:All calculations are subject to large and careless errors and should be checked). Edison (talk) 20:04, 26 June 2010 (UTC)
 * Ballistics calculations done with energy are usually misleading. You usually can't get anything but a tiny tiny fraction of the energy you use as kinetic energy of the craft, because almost all the energy is carried away in the other direction by the reaction mass.  If you use a solar sail, the "reaction mass" is the photons bouncing off the sail (note that it doesn't help to absorb them instead; you get worse results that way).  Solar sails do get better from this perspective as you approach the speed of light away from the light source, because the reflected photons are red-shifted and therefore don't carry away as much of the energy.  --Trovatore (talk) 20:30, 26 June 2010 (UTC)
 * But, if you're relying on the last effect to bail you out once you get near the speed of light, keep in mind that this is giving you improved increase in kinetic energy per unit time in the Sun's frame of reference, not the ship's. From the perspective of the ship, the light from the Sun is red-shifted, and is therefore providing less thrust. --Trovatore (talk) 20:35, 26 June 2010 (UTC)


 * You could also consider using a laser-driven solar sail. With no reaction mass having to be stored on-board, you don't have any of those nasty restrictions.  You can use just one solar sail for the first half of the journey - then when you are halfway there, you release the connections between craft and sail and deploy a second solar sail behind you.  The laser light from back home must then hit the original (now disconnected) sail - uselessly accelerating it towards your destination at ever increasing speeds.  However, if the first sail is mirrored, the light can bounce off of that and back towards your craft and its second solar sail.  That allows you to decelerate throughout the second half of your trip...and perhaps even return home again.  Additionally - instead of using a true laser - you could build a gigantic lens system and focus sunlight directly onto your craft.  The lens would have to continually and microscopically adjust its focal length as the vehicle gets further away.  There are undoubtedly vast problems with building large enough lasers, lenses or mirrors, but those are not issues of fundamental science - they are engineering and financial issues that could probably be overcome given the willpower to do so.  However, it's hard to imagine anyone funding such a crazy effort. SteveBaker (talk) 05:57, 27 June 2010 (UTC)


 * There are some similar questions here, question 7.5 on page 13 is actually about a mirror propelled by a laser. I'm wondering though about how to deal with the fact that a laser beam will always diverge. If the initial beam of the photons appearing out of the laser is L, then the uncertainty in the momentum of the photons perpedicular to the beam direction will be of order hbar/(2L) at best. Dividing this by the momentum in the direction of the beam of h/lambda, gives an angle of divergence of lambda/(4 pi L). You can think of this as giving the width of the peak of the inteference pattern if you were to shine the laserlight on a far away screen. I don't see how one can make this angle arbitrarily small. Count Iblis (talk) 15:01, 27 June 2010 (UTC)
 * You don't necessarily have to deal with the divergence - after all, the only problem with that divergence is that a lesser percentage of the energy you put into laser ends up propelling the spacecraft rather than shooting off uselessly into space. But since the laser can stay back here in our solar system, we can make it larger to compensate for the wastage due to divergence without making the spacecraft bigger or heavier.  If we can build one big solar-powered laser, then we can (in principle) build 100 of them...or 1000 or whatever it takes to deliver enough energy on target.  That's why it's only an engineering/economic problem - not a matter of fundamental physics.  Similarly, we can make the solar sail larger - if one square kilometer isn't enough - why not make one 10 times bigger and have 1000 square kilometers?  Again, it's an engineering issue - not a matter of fundamental physics. SteveBaker (talk) 01:49, 28 June 2010 (UTC)


 * There has been some distinction between "physical impossibility" and "engineering limitation" - this is a valid distinction to draw. However, we need to make clear that we do not know about some physical possibilities and impossibilities until our engineering capabilities bring us into the regime where those physical laws will start to manifest, so that we can do controlled experiments.  For example, it would not have been possible to know that the speed of light was finite until we were able to build machinery precise enough to measure it.  So, our ability to develop correct physical theories (and deduce physical impossibilities) was limited by our engineering capability.  After we started measuring that the universe behaved in certain bizarre ways, we developed consistent equations and physics to describe those behaviors.  I think it is fair to say that there may be as-yet-undiscovered limitations (and possibilities) related to interstellar travel that we currently have no physics to describe.  Once we start building giant lasers and spacecraft, we may learn new details about relativistic phenomena.  Material properties, fundamentals of energy transfer, and so on, all plausibly might need to be rethought and re-understood in this new regime.  Nimur (talk) 20:49, 27 June 2010 (UTC)

Production of Mn oxide
What is the chemical equation if you heat Manganese oxalate hydrate in a crucible in the presence of oxygen?

--478jjjz (talk) 04:11, 26 June 2010 (UTC)
 * I have done this experiment. The product is Mn (II) Mn (III) oxide = Mn Mn2 O4 I just need to use mass % to figure out the coefficients.--478jjjz (talk) 05:33, 26 June 2010 (UTC)


 * Manganese(II) oxalate hydrate is Mn(C2O4).2H2O (or sometimes Mn(C2O4).3H2O)
 * The first step is dehydration:
 * Mn(C2O4).2H2O → Mn(C2O4) + 2H2O
 * The decomposition in air gives Mn2O3 without any carbon monoxide (see )
 * Mn(C2O4) +¾O2 → ½Mn2O3 + 2CO2  (equation 1)
 * Manganese(II,III) oxide is formed when Mn2O3 is heated, some oxygen is lost:
 * 3Mn2O3 → 2Mn3O4 + ½O2  (equation 2)
 * Combining equations 1 and 2 gives:
 * 3Mn(C2O4) + 2O2 → 6CO2 + Mn3O4
 * So the overall reaction is


 * 3Mn(C2O4).2H2O + 2O2 → 6CO2 + Mn3O4 + 2H2O


 * 77.86.115.159 (talk) 14:18, 26 June 2010 (UTC)


 * I kowtow before thee. Your response was thorough and simply phenomenal. Thank you.--478jjjz (talk) 02:53, 27 June 2010 (UTC)
 * No need, we are here to serve .. 77.86.115.159 (talk) 03:05, 27 June 2010 (UTC)
 * In a vacuum it will form manganese(II) oxide. --Chemicalinterest (talk) 18:25, 27 June 2010 (UTC)

Ion nomenclature
In Manganate, shouldn't hypomanganite and manganite be switched? Because it should go hypo-ite, -ite, -ate then per-ate, like the chlorine oxoanions.--Mikespedia is on Wikipedia! 07:26, 26 June 2010 (UTC)
 * This is most likely a typo in the article! Thanks! I will change it.--Stone (talk) 08:06, 26 June 2010 (UTC)
 * Wait...then is potassium manganite a typo?--Mikespedia is on Wikipedia! 09:59, 26 June 2010 (UTC)
 * Manganate(V) is hypomanganate, not hypomanganite. The potassium manganite article is just plain wrong, I'll try to fix it in a moment. Physchim62 (talk) 11:08, 26 June 2010 (UTC)
 * Actually, it was only one sentence which was obviously wrong in potassium manganite, removed now. Physchim62 (talk) 11:32, 26 June 2010 (UTC)
 * Manganites can also refer to mixed oxides of manganese and other metals (eg ). The mineral manganite is MnO(OH), a slightly hydrated form of Mn2O3. Physchim62 (talk) 11:32, 26 June 2010 (UTC)
 * So now what are the correct names?--Mikespedia is on Wikipedia! 12:36, 26 June 2010 (UTC)
 * IUPAC proposes permanganate, manganate(VI) and manganate(V), along with the systematic names tetraoxidomanganate(1−), tetraoxidomanganate(2−) and tetraoxidomanganate(3−). Physchim62 (talk) 12:58, 26 June 2010 (UTC)
 * So how about the trivial name?--Mikespedia is on Wikipedia! 13:26, 26 June 2010 (UTC)
 * give "hypomanganate" as a trivial name for managanate(V), as does . The latter reference (which I've only just looked up) also refutes the potassium manganite article: apparently, the compound formed by the dissolution of manganese dioxide in concentrated potassium hydroxide is K3MnVO4 (by disporportionation), ie potassium hypomanganate. Physchim62 (talk) 13:35, 26 June 2010 (UTC)
 * I've corrected potassium manganite, which now redirects to potassium hypomanganate. Physchim62 (talk) 15:29, 26 June 2010 (UTC)
 * ... manganite is a IV species, I've put Potassium manganite up for speedy deletion. Potassium hypomanganate seems fine.77.86.115.159 (talk) 16:17, 26 June 2010 (UTC)
 * Mixed metal oxide manganites do exist - I've created a temporary hat note from manganite.
 * These are quite notable eg - if anyone wants to create an article about these compounds please do. They appear to be of interest due to their magnetic properties ie Computer hard disk=$$$ eg  There really should be an article on these...Sf5xeplus (talk) 17:03, 26 June 2010 (UTC)
 * Lanthanum strontium manganite already exists, although it's not in wonderful shape. Physchim62 (talk) 18:28, 26 June 2010 (UTC)
 * Mixed-valence is currently a redirect to inner sphere electron transfer, an article that does talk about mixed-valence compounds. Seems the relevant section or two could split out into its own article and extended on this topic. DMacks (talk) 17:17, 26 June 2010 (UTC)
 * Yes, indeed. Those mixed valence manganites seem to be based on manganese(III) compounds which are doped to give some manganese(IV). Interesting, there is a potassium compound, K6Mn2O6, which contains discrete Mn2O$6− 6$ anions : I would call that compound potassium dimanganite. The lithium and sodium manganites, MMnO2, are mixed oxides with a distorted NaCl structure. Physchim62 (talk) 17:19, 26 June 2010 (UTC)
 * So now they go permanganate, manganate, hypomanganate and hypomanganite?--Mikespedia is on Wikipedia! 02:47, 27 June 2010 (UTC)
 * And how about manganate(IV)?--Mikespedia is on Wikipedia! 02:50, 27 June 2010 (UTC)
 * Not quite:
 * +7 permangante
 * +6 manganate
 * +5 hypomanganate
 * +4 would be manganite - if we had a good example..
 * +3 would be hypomanganite ... These are for oxo-anions - for metal oxides in general people call them manganates or manganites irrespective of oxidation state.. (sometimes they get it right, and call Mn3+ a hypomanganite, but not often..)
 * Or just use manganate(n)
 * It's all described here
 * 77.86.115.159 (talk) 03:08, 27 June 2010 (UTC)

Eating late leads to weight gain?
I know it's repeated a lot by non-scientific sources (cover of magazines) but can anyone point me towards some scientific sources, or something similar, that discuss if eating before going to sleep increases weight gain (than eating the same diet, but only at a different time)? Shadowjams (talk) 07:39, 26 June 2010 (UTC)
 * I don't know of any such sources, but I'm butting in just to point out that this is not, in my opinion, really the right question. The right question is, if you schedule your evening meal early vs late, will that make a difference in your weight?  You can't assume that your dietary intake will be the same in the two scenarios.  It's possible that one of them will make you overall hungrier than the other. --Trovatore (talk) 07:43, 26 June 2010 (UTC)
 * I understand the distinction you're making, and my question is the original one. I'm interested in the nutritional / metabolic question rather than the public health considerations. You bring up a good point though: that though may be the reason for so much popular culture repetition of that statement. From a public health perspective the causation is less important than the correlative effect. Shadowjams (talk) 08:34, 26 June 2010 (UTC)
 * Oh, no, it's still causation. Just with an extra link in the causal chain.  Correlation could be an indication of causation in the other direction, or a common cause for the two effects; that's not what I'm talking about. --Trovatore (talk) 09:16, 26 June 2010 (UTC)
 * Here's a BBC article which is about breakfast size. It makes it sound like a behavioral thing, as you say. But wait! Here's a more recent one  about eating late at night, which makes it sound metabolic (and highly speculative). 213.122.29.174 (talk) 11:16, 26 June 2010 (UTC)


 * I remember hearing that there was a study that claimed people who ate more at night were fatter than people who didn't, but then subsequent investigation showed that the study hadn't properly looked at how much people were eating the rest of the time, so really all the study showed was that people who ate more tended to be fatter. I can't find this story, however. 86.164.57.20 (talk) 14:32, 26 June 2010 (UTC)


 * Well, a lot of bodybuilders will have a late night shake since they believe it'll prevent muscle breakdown. TheGoodLocust (talk) 17:38, 26 June 2010 (UTC)


 * Thank you all. That BBC link seems to sum up my instinct, "At this stage, the results could still be interpreted as controversial when applied to humans." Maybe I need to spend some quality time on pubmed. Shadowjams (talk) 09:18, 27 June 2010 (UTC)

Sensing colours
What causes the difference between sensing colours in a coloured material and in coloured light? For example, to me, a reddish violet colour reflected from some material looks delightful, but exactly the same colour being displayed by a computer screen looks very different, even some disgusting. Is that a matter of a colour system or does the brain perceive the information differently? --87.95.51.116 (talk) 13:22, 26 June 2010 (UTC)
 * By "exactly the same" colour you mean that you perceive the same colour whereas colours can have very different spectra but seem the same. The colours on a computer screen have to be made from the 3 available primary colours and they limit the range of possible colours. In the case of a material one's perception is affected by knowing that the surface has a texture that can be touched. Cuddlyable3 (talk) 14:05, 26 June 2010 (UTC)
 * Other factors that may explain the difference you perceive are that the screen image flickers, and the material is lit by ambient light of a certain colour for which you unconsciously compensate. Cuddlyable3 (talk) 14:11, 26 June 2010 (UTC)
 * See gamut for the technical details of how our eyes respond to colour, and the limited range most monitors have. CS Miller (talk) 16:05, 26 June 2010 (UTC)
 * When you look at a colored material, the light reaching your eye is determined by a combination of the color of the material and the color of the illumination, but your visual system automatically subtracts the color of the illumination, to such a high degree of perfection that we are generally not even aware of the process. When you look at a colored monitor, the visual system again attempts to compensate for illumination, but the result is very different.  Thus you really aren't seeing the same thing at all in the two cases.  In fact it isn't ever correct to say that a material has the same color as a light unless the lighting conditions have been precisely calibrated, and even then a small change in lighting will cause the appearances of the two to diverge. Looie496 (talk) 04:18, 27 June 2010 (UTC)
 * Some considerations are:
 * The aesthetic effect of a slight texture.
 * Shiny reflections (particularly highlights). On hard, rough surfaces such reflections will be fragmented, but still present.
 * The reflection of light (which may be strongly coloured) from other nearby objects. 3D artists know this as radiosity, and it is important to realism and prettiness.
 * Related to this is that parts of the object further away from other objects (or walls) will be more brightly lit. This has an effect even when the object is viewed close-up. Outside of computer screens, we rarely encounter objects which present areas of flat colour of a single tone (and just as well, because it would be confusing.) We don't tend to be conscious of this, though, and I think it might be the effect most important to your question - surfaces which appear to be a single tone really aren't. You can verify this by taking photographs and inspecting them digitally.
 * In artificial light, the parts nearer the light source are more brightly lit (because of the spread of the light).
 * Internal illumination of a surface can make the whole thing glow (this would tend to make it more similar to a flat colour on a computer screen, though). Transparency and refraction may matter.
 * Oddities of various materials which cause tone and hue variations depending on the angle of the surface (or a local part of it) to the eye. The pile of velvet produces an effect similar to lenticular printing. Some materials are iridescent.
 * 213.122.13.154 (talk) 11:02, 27 June 2010 (UTC)

toxic to fish ?
There was an NPR story[6] this morning about the use of Dawn dish detergent in the BP oil spill.

arent soaps toxic to fish ? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 17:49, 26 June 2010 (UTC)


 * This does not directly address your question, but presumably the soap is used to clean aquatic birds, like pelicans, and aquatic mammals, rather than fish. -- Jayron  32  17:56, 26 June 2010 (UTC)


 * Yes. Conventional soaps (soap bar) are harmful because they reduce the level of oxygen in the water. Liquid detergents are similarly harmful; they also damage the fishes gills, as well as they eggs, and make the absorption of toxic chemicals more likely.
 * Old fashioned detergents, and laundry detergents are also toxic to fish for other reasons - lowering pH and presence of phosphate causing algae blooms. (not all algae blooms are harmful, but some are)
 * It's summarised here in the third section. that's about freshwater, but it's similar for marine as well
 * Also see http://www.sciencedaily.com/releases/2009/03/090316101430.htm 77.86.115.159 (talk) 18:13, 26 June 2010 (UTC)


 * If you are refering to this NPR story, Dawn dish detergent is used more on birds and turtles and such, an example being the Pelican pictured here.


 * "Dawn spokeswoman Susan Baba says ... the reason Dawn is so good at cleaning birds without hurting them is that it was designed to erase grease from dishes without harming hands. The exact formula is a secret, but she says the key is balancing the surfactants — the chemicals that cut the grease." Dunno if that helps clarify anything. :) Avic enna sis @ 18:49, 26 June 2010 (UTC)
 * It's important to note that there are 2 types of detergent being used here:
 * Dawn : used to clean birds etc - this is being used (I assume) on land, and may not come into contact with fish
 * 'Oil dispersants': these are the 'detergents' that are used at sea to disperse the oil slick, they are toxic to fish (as is the oil, fundamentally)
 * 'Dawn' isn't being poured directly into the Gulf of Mexico as such.77.86.115.159 (talk) 19:16, 26 June 2010 (UTC)

Life expectancy in the UK
A newspaper says "He [UK politician] pointed out that in 1940, when the retirement age was set at 60 for women and 65 for men, life expectancy was 72. Today it has soared to 89 for men and 90 for women". Is there any truth in the latter claim in particular? Thanks 92.15.5.103 (talk) 19:56, 26 June 2010 (UTC)
 * Seems No. See http://www.statistics.gov.uk/cci/nugget.asp?id=168, there is more detailed data in the links on that page.77.86.115.159 (talk) 20:03, 26 June 2010 (UTC)


 * It's possible that this is a statistical balls up (where did you read it)?
 * eg http://www.independent.co.uk/news/uk/politics/mens-pension-age-up-to-66-from-2016-2009087.html appears to be confusing percentage expectancies of reaching 65 years and life span - ie 90% of women live to be 65? Is that what you got? 77.86.115.159 (talk) 20:09, 26 June 2010 (UTC)
 * City AM, 25th. June 2010, page 9. 92.15.5.103 (talk) 21:40, 26 June 2010 (UTC)
 * Doesn't look like misreporting - the govermental site gives the same words.77.86.115.159 (talk) 22:19, 26 June 2010 (UTC)
 * http://www.dwp.gov.uk/newsroom/ministers-speeches/2010/24-06-10.shtml repeats similar - looks like the minister's speech contains an error if the goverment statistics are to be believed - I'm fairly certain someones balls up their table.77.86.115.159 (talk) 20:13, 26 June 2010 (UTC)


 * Having had a quick look at the data it definately seems that ~90% of people can expect to live to 65 in the UK .. this appears to be the truth (though the male female difference appears to be ~5% not 1% ..as of 2006-8 see interim life tables). 77.86.115.159 (talk) 21:04, 26 June 2010 (UTC)

On BBC World the figure of 89/90 years was also mentioned, but it was said that some who is 20 years old now can expect to live that long. Count Iblis (talk) 00:12, 27 June 2010 (UTC)


 * That seems rather optimistic and assumes the UK's economy and technology will progress at the same rate - much less regress.TheGoodLocust (talk) 01:11, 27 June 2010 (UTC)
 * Actually, it probably assumes no progress at all. Any attempt to factor in future progress involves lots of guesswork, so it usually isn't done. They calculate these probabilities by assuming that the chance of the person in question dying during the year when they are X years old is the same as the proportion of people that were aged X a year ago that died during the last year (actually they usually average over 3 years or so, but that isn't important). So, it's how long you could expect to live if stuck in a time loop living the last year again and again. The figure is wrong, though. The Office of National Statistics (see the interim life tables linked to above) says a man aged 20 can expect to live to 78 and a woman to 82 (that's less than a year older than expectancy at birth, since we've all but eliminated infant mortality in the UK - the chance of a child dying before turning 20 is tiny). I don't know what BBC World was talking about. --Tango (talk) 13:38, 27 June 2010 (UTC)
 * Perhaps for this purpose (finding a good argument for increasing the pension age), the government asked the people doing to calculations to be less conservative and make some reasonable assumptions about progress in medicine? Count Iblis (talk) 14:32, 27 June 2010 (UTC)
 * It's possible, but if it were possible to make such reasonable assumptions why wouldn't they always be used? Life tables are mostly used for determining fair values for pension schemes and life insurance policies, and people doing such calculations would have exactly the same requirements from their data as people wanting to work out a fair retirement age. --Tango (talk) 16:20, 27 June 2010 (UTC)

Calcium Hypochlorite
I have about 10 kg left of dry powder bought as Calcium Hypochlorite three years ago. It is in a non air-tight (but child proof) plastic container and seems to have lost its zing. So does this slowly decompose to CaO in air? The WP article only lists reacting with CO2 and I cannot believe enough of that has got through the container lid. Roughly how long can I keep it if I get some more (so how much should I buy)? The large compact tablets of presumably the same thing were airtight sealed and seem to have lasted better. --BozMo talk 21:13, 26 June 2010 (UTC)
 * This book page 523 mentions that the stabilily is reduced by absorbed water content, and that typical compositions loose about 3-5% effectiveness per year. This  states that it 'rapidly decomposes on exposure to air' and 'liberates chlorine with water' - so a non air tight container, especially in a damp enviroment will go off eventually.
 * It seems unlikely that 10kg has gone off.. I recommend removing some from the top of the container, and seeing if it's better lower down.77.86.115.159 (talk) 21:48, 26 June 2010 (UTC)


 * The decomposition in air at room temperature is not totally straightforward, some chlorine will be evolved, but not all - roughly Ca(OH)Cl 'basic chloride' is roughly what is left over from:
 * 4Ca(OCl)2 + 2H2O >> 4Ca(OH)Cl + 3O2 + 2Cl2
 * though a variety of reactions can occur including a slow reaction which increases the acidity, which in turn increases the above decomposition
 * 3Ca(OCl)2 >>  2CaCl2 + Ca(ClO3)2
 * So once the stuff starts to go off, it tends to go off faster and faster.. The best bet is to keep it in a dry place, out of light and heat, and keep it dry.77.86.115.159 (talk) 22:07, 26 June 2010 (UTC)

Relatively high incidence of lactose tolerance in Spaniards
Why do Spaniards have relatively high lactose tolerance in comparison to their neighbors? --Belchman (talk) 21:50, 26 June 2010 (UTC)
 * I wasn't aware that they do. In various group studies I've seen, the southern French and Portuguese populations have had higher percentages of lactose intolerance.  . As with most things generically related, I suspect fluctuations in prevalence is a result of how often those genes are used. In populations where lactose intolerance is higher, it's reasonable to assume that either lactose was less available to them, or they didn't have it quite as much. Regards, --— Cyclonenim | Chat  21:58, 26 June 2010 (UTC)
 * The article Lactose intolerance describes what is known about its cause and distribution. Cuddlyable3 (talk) 22:01, 26 June 2010 (UTC)

automotive question
What is minimum PSI cylinder compression pressure for 1275cc engine in a MG Midget?
 * Thanks . . . Joe
 * I removed your email address so you don't get spammed. Ariel. (talk) 04:10, 27 June 2010 (UTC)
 * I removed your email address so you don't get spammed. Ariel. (talk) 04:10, 27 June 2010 (UTC)

Opal vs clear in old incandescent bulbs
What difference did 'opal' or 'clear' finish make to the light in old incandescent bulbs? Was one more white than the other? --78.148.142.76 (talk) 22:25, 26 June 2010 (UTC)
 * clear was more efficient, but a pain to look at so you would want it in a light fitting.  Whereas the opal did not blind eyes seeing it, so it is more suitable for the bare globe.  Strangely Incandescent light bulb does not mention it. Graeme Bartlett (talk) 22:30, 26 June 2010 (UTC)
 * Yes, the 'opal' is/was just a Diffuser (optics) - didn't really affect the colour.77.86.115.159 (talk) 22:37, 26 June 2010 (UTC)
 * I never heard of diffuse white bulbs being called "opal". Must be a UK thing.  If someone gave me an "opal" bulb I would probably be expecting it to be pink or something. --Trovatore (talk) 23:14, 26 June 2010 (UTC)


 * I've generally seen it as short for opalescent, rather than a direct reference to opals. If that helps at all... 86.164.57.20 (talk) 01:57, 27 June 2010 (UTC)


 * The first incandescent light bulbs were clear glass, but were often placed in frosted glass fixtures to decrease the glare. "Ground glass" had a surface which had literally been made rough by sanding or etching. "Frosted" was a term used more commonly than "opal" for early light bulbs which diffused the direct glow of the filament as in this 1904 citation. Here is a 1902 description of "opal glass" as then used in shades for gas lights: .Here  is a 1913 House and Garden article about opal or frosted glass shades around lights. Here is a 1911 engineering article which discusses frosted, etched and opal glass to diffuse illumination. They likely used a clear bulb in a diffusing globe. They were probably slightly less efficient than clear bulbs. A later term was "soft-white."  Modern frosted or soft white bulbs are likely to have a water-soluble white coating inside the bulb, rather than it being actually etched by acid or sandblasting as in early frosted bulbs. The color temperature of the light would have been somewhat independent of the forsted or clear bulb, and would have been related to the design efficiecy and lifetime of the filament. I expect that the frosted or clear light bulb would not have been tinted blue as in modern "full spectrum" bulbs, but would have had a typical somewhat yellowish appearance of incandescent bulbs. Edison (talk) 03:24, 27 June 2010 (UTC)
 * Probably a UK thing as trovatore says - opal or clear over here .. |countryGB&cr=countryUK|countryGB&sa=X&ei=gckmTIyyHJz20wTUjPXCBA&ved=0CBEQpwU google shopping.77.86.115.159 (talk) 03:48, 27 June 2010 (UTC)
 * I don't know where "over here" is to you but in the States, we generally have a choice between clear and "soft white" which I think is what everyone seems to be calling "opal". Dismas |(talk) 08:51, 27 June 2010 (UTC)
 * UK, should have been clearer - thought link to google.co.uk would be obvious, but on second thoughts, it's not —Preceding unsigned comment added by 77.86.115.159 (talk) 12:10, 27 June 2010 (UTC)
 * Tip: If you click on the first link in an IP signature, it takes you to the contributions page for that address. At the bottom of that page there's a link called "Geolocate", which will show you where the post comes from (well, usually and approximately; there are a few gotchas). --Trovatore (talk) 10:14, 27 June 2010 (UTC)

Power supply to the town sewage works
Today I took a stroll down to my local sewage works (life in the fast lane, huh), and the overhead electrical supply to it caught my attention. I've taken a couple of photos of the utility pole outside - photo A and photo B. I have two questions: Any ideas? Thanks. -- Finlay McWalter • Talk 23:14, 26 June 2010 (UTC)
 * Firstly, what are the characteristics of that electrical supply likely to be (this is in the UK). It's surely three-phase, and of a fairly high voltage (the pole is ~25ft tall, with some serious anti-climb measures and lots of warning signs about carrying high objects nearby). I believe high-users like this in North America get either 13kV or 4kV - what would such a facility typically get in the UK? (It's a pretty big site, with several acres of tanks, serving a town of around 10,000 people).
 * Secondly, what that is that little light thing, that's best seen in photo B? It's about ten feet off the ground, it carries the legend P360-alpha, and there's no cable running to it.  I'm guessing it's a warning light - that somehow being near the pole with a conducting thing like a ladder causes enough flux for this thing to light up as a warning.  Frankly it's not in a place I'd feel happy about visiting in the dark, so I can't discount that it's simply a solar-powered lamp (or somehow powered by the field of the transmission line) so that it illuminates the "danger of death" signs at night.
 * A. Three phase obviously 11 or 33kV are standards
 * Images from geograph.org 11kv 33kv lloks like yous is 11kv, though that is an uneducated guess - there should be standards for UK power line construction somwhere on the web. Haven't found them yet. (It seems there are some other voltages used 6.6kv as well).
 * this link has some typical images.
 * B. why don't you get a lightweight aluminium ladder and have a closer look at the light just kidding. If it's solar powered then you should be able to see the solar cell using a mirror attached to a fishing rod Maybe not. A safe way to see it to attach a video camera to a kite and then fly it above the device No. Sorry can't help myself. Don't know.77.86.115.159 (talk) 23:58, 26 June 2010 (UTC)
 * The "little light thing" has a wide-angle globe, so it looks like an illumination lamp to illuminate the warning signs and/or light up the area for linesmen to work at night. I can't tell how it's powered, but if we're talking about an 11-kV 50-Hz power line, then there's no way you could get enough flux through the air to power the lamp, not even with a bucket truck nearby for conductance -- so it can't be a warning light like you say, nor can it be powered by the field of the power line.  FWiW 67.170.215.166 (talk) 05:50, 27 June 2010 (UTC)
 * The "P360 Alpha" gadget is lightly built and poorly attached to the pole, with one screw per side. It has no wires going to it. If it were a solar light I would not expect it to put out much of a light overnight, or after a few overcast days. It looks like a plastic cylinder, with a lid to keep rain out (can't rule out a solar collector on the top, but is is not optimally aimed for any latitude but the equator). At the resolution available, the bottom looks like it might be a basket with fine openings, which would keep out birds but let in bugs and air, so I wonder if it might be a non-utility gadget used on the pole with permission of the utility for sampling what bugs are in the area, or for air quality monitoring. They would periodically come along and collect the sticky paper inside or see what wandered into an internal trap, or what passed through filter paper. Edison (talk) 20:45, 27 June 2010 (UTC)
 * Along those speculative lines - maybe it's designed to trap bugs that might otherwise eat the wooden pole? (I sense this is far from likely)83.100.183.236 (talk) 20:49, 27 June 2010 (UTC)
 * I doubt that. Poles are usually treated with serious preservatives. If my speculation about a trap for studying what the insect population is (rather than eradication) it might have a solar powered UV led to attract insects at night. Some insect study traps are triangular paper prisms with sticky paper inside, others are plastic cylinders with an attractant inside and a funnel trap to prevent escape. Edison (talk) 20:53, 27 June 2010 (UTC)
 * Applying Occam's razor, it seems likely that the light was installed but wires were never connected to it (or were removed later) so it is not operational. On the other hand, other photos of the P360 Alpha also lack wires.  Maybe the light is battery-operated.  Nimur (talk) 21:01, 27 June 2010 (UTC)
 * As it appears to have a transparent lid, I'd suggest that it is solar-charged darkness-activated light. —Preceding unsigned comment added by Csmiller (talk • contribs) 21:11, 27 June 2010 (UTC)


 * Thanks to everyone for your observations so far. Some clarifications (which aren't intended to cast aspersions on your inventive ideas, but probably will anyway). Yes, it's just like Nimur's Flickr photo - the underpart is definitely either glass or plastic (it's not a wire mesh). The line runs N-S and the P360 was attached to the south facing surface. As the only approach is from the east, I wouldn't think this was the best location for a warning light. This is in Northern England, which means solar power is pretty unlikely to be effective for a light, particularly in the winter. The UK doesn't have much in the way of serious wood-eating insects (no termites or army ants and relatively few beetles), so I'd be surprised if this was its purpose. I guess it could be for collecting insects for some kind of survey, but it's well above the anti-climb barbed attachments and clearly in the danger zone, so I'd guess that if that is its purpose, it must be there necessarily (that is, it's studying the effect of the power lines on insect behaviour) - there are plenty of fence posts, lamp standards, and telephone poles at which a study unrelated to electricity could be undertaken.  The land surrounding its location is the aforementioned sewage plant, some playing fields, and a farm. A stream runs to the west. I still think (without any evidence) that it's to do with safety (given its intrinsically unsafe location). Perhaps if someone does accidentally bridge the overhead lines to ground, this thing flashes or wails, warning the others in that worker's party that they mustn't touch their stricken colleague. -- Finlay McWalter • Talk 21:48, 27 June 2010 (UTC)
 * But how can it sense that the line has been shorted if it's not connected to it in any way? No, it can't be a sensor -- it's prob'ly there for illumination (e.g. to illuminate the "Danger of Death" warning signs). FWiW 67.170.215.166 (talk) 01:36, 28 June 2010 (UTC)
 * Putting it on the S side of the in England is consistent with solar cells on the top. Have you noted whether it lights up visibly at night? I liked the idea of plastic mesh at the bottom to exclude birds and collect a sample of collect insects, but if it is plastic with no holes some sort of light or warning device seems like a good explanation. I think it looks really flimsy and lightly built to be permanent utility equipment. It would also get severely in the way of a worker climbing the pole, since he would have a belt going around the pole opposite the side the gaffs in his boots dug in. The top could be a solar collector and the bottom an LED light, but the middle seems rather large just to hold the batteries. I have not been impressed with the usefulness of solar lights, since a few cloudy days greatly decreases their ability to stay lit all night, and a warning light only on for part of the night seems useless. A light which comes on when it senses someone near, or with a motion sensor, might work better, or a light which comes on when it has detected a surge of current in one of the lines overhead might be useful as a fault indicator to help locate where a line fault occurred. It could be triggered by a transmitter in a passing utility truck after a line fault, and light up if it detected the current surge. This would go quicker than present fault indicators, which only have a little indicator which shows red when a fault current has passed it, but which take a slower examination with binoculars. (Or it could be a hanger for a miniature UFO). Edison (talk) 19:07, 28 June 2010 (UTC)
 * (I am On FIRE these past few weeks at the RefDesk!) I'm in the industry so lucky I have the answers at hand. First answer first: the rule that we use is "11kV per shed, plus one shed extra". The insulators in your photos (those glass discs) have two sheds (discs) and are therefore 11kV (the UK uses 11kV). Second answer: the device is a fault path indicator, Googling that term I found the EXACT device in your photos at the manufacturer's website which also describes the principle of operation. QED :) Zunaid 19:38, 28 June 2010 (UTC)


 * Splendid, that's plainly it exactly. What a clever idea - I'd imagine that flashing should be visible from a helicopter, making locating a fault on a long countryside line much more tractable (would that such a system had existed to diagnose failures in cheapernet, back in the day).  If someone more electrically knowledgeable that myself wants to take a stab at writing a fault path indicator article, I'd be happy to tramp back out to the sewage works (depending on which way the wind blows) with a decent, zoomable camera to take some more worthwhile shots of it.  Thanks to Zunaid, and to everyone for your imaginative suggestions. -- Finlay McWalter • Talk 20:25, 28 June 2010 (UTC)


 * Even better than that is to have it on supervisory i.e. it communicates back to the control centre remotely (via radio, GPRS, power line carrier, fibre optic etc.) so that we can see first time where the fault is and dispatch the operator to only patrol that part of the line. I'll have a stab at creating a stub sometime in the coming days, just a bit busy at the moment. Zunaid 07:54, 29 June 2010 (UTC)